PROBLEM TO BE SOLVED: To provide an imaging device and capsule endoscope that include an image formation optical system in which the image formation optical system is advantageous to a correction of a chromatic aberration without making a Petzval sum of an optical system small, is easy to have the number of lens pieces reduced and to be downsized, and can obtain an excellent optical performance.SOLUTION: An imaging device comprises: an image formation optical system that includes a brightness stop S determining an axial light flux, and a diffraction optical plane being arranged at a position different from an arrangement position of the brightness stop S； and an imaging unit that is arranged on an image side of the image formation optical system, and includes a light reception surface of a non-plane curved concavely toward the image formation optical system, and the diffraction optical surface is arranged at a position satisfying a conditional expression (1). 0.1<；DSD/TL≤1.0...(1), where TL is a real distance from an incidence surface of the image formation optical system on an optical axis of the image formation optical system to the light reception surface thereof, and DSD is a real distance between the position of the brightness stop on the optical axis of the image formation optical system and the diffraction optical surface. When a focal length of the image formation optical system is variable, the conditional expression (1) is a conditional expression in a wide angle-end state.SELECTED DRAWING: Figure 1【課題】光学系のペッツバール和を小さくする必要が無く、色収差の補正に有利で、レンズ枚数の低減や小型化も容易で、良好な光学性能が得られる結像光学系を有する撮像装置及びカプセル内視鏡を提供する。【解決手段】軸上光束を決める明るさ絞りＳと、明るさ絞りＳの配置位置とは異なる位置に配置された回折光学面と、を有する結像光学系と、結像光学系の像側に配置され、結像光学系に向けて凹状に湾曲した非平面の受光面Ｉを有する撮像部と、を有し、回折光学面は、条件式（１）を満足する位置に配置される。０．１＜｜ＤＳＤ／ＴＬ｜≦１．０…（１）、ここで、ＴＬは、結像光学系の光軸上における結像光学系の入射面から受光面までの実距離、ＤＳＤは、結像光学系の光軸上における明るさ絞りの位置と回折光学面との間の実距離であり、結像光学系の焦点距離が可変の場合は、条件式（１）は広角端状態での条件式である。【選択図】図１
